1. Field of the Invention
The present invention relates to an apparatus and an improved process for recycling used glycol-based engine coolant.
2. Description of Related Art
Engine coolants are used to protect internal combustion engines from temperature extremes. The coolants employ ethylene glycol with or without propylene glycol to lower the freezing point and raise the boiling point of water in internal combustion engines. These coolants also commonly employ corrosion inhibitors to counteract the corrosion associated with engine coolants. The coolants typically contain ethylene glycol, with or without propylene glycol, at a concentration of about 30 to 70% by volume, and corrosion inhibitors at approximately 1 to 3% by weight.
The American Society of Testing Materials (ASTM) sets recognized industry standards for the components of engine coolants, both virgin and recycled. The Maintenance Council (TMC) of the American Trucking Association also sets recognized standards for engine coolants.
The useful life of engine coolants is limited by the degradation over time of the glycol and inhibitor components. The glycol components (ethylene glycol with or without propylene glycol) chemically break down into various undesirable organic acids. The accumulation of these acids lowers the pH of the engine coolant composition from an initial pH of approximately 10. When the pH decreases below approximately 8.3, aluminum, steel and iron corrode, weakening the components that they comprise and resulting in eventual component functional failure. In heavy-duty applications, the necessary and commonly practiced addition of supplemental coolant additives (SCAs) increases the total dissolved solids (TDS) in the coolant until a saturation threshold is approached, at which point severe engine damage is probable. Coolant with excessive TDS is associated with premature failure of radiators, water pumps and other cooling system components. Copper and brass also corrode upon extended exposure to engine coolant. In addition, the lead solder in radiators can degrade into lead oxide, eventually allowing leaks to develop in the coolant system heat exchangers.
Because of the well-established corrosive effects of the circulating coolant, initial corrosion inhibitors and SCAs are conventionally added directly to the engine coolant. However, with time the inhibitors are consumed, allowing the corrosive effects of the engine coolant to damage the entire cooling system. Implementation of certain maintenance procedures is necessary to prevent such damage. The most common procedure is removal and replacement of the engine coolant after a pre-established time or service interval. In some instances cooling system additives, which are usually alkaline and include SCAs, are directly added to the coolant to extend the protective properties, decrease the corrosive effects, and postpone replacement of the coolant.
Recycling used engine coolant has become increasingly desirable due to two significant factors. First, engine coolant frequently merits designation as a hazardous waste under the Federal Clean Water Act. Federal and some state environmental protection agencies have instituted strict regulation of the disposal of used engine coolant. In some cases the disposal of engine coolant requires imposition of waste disposal fees and surcharges. Second, ethylene glycol, the principal cost component of engine coolant, has become more expensive. Dramatic price fluctuations and significant shortages in the supply of ethylene glycol have occurred. Therefore, there are both environmental and economic pressures to recycle engine coolant and recover the glycol component in an efficient and cost-effective manner.
A number of processes and systems have been advanced as possible commercially viable solutions to the problem of recycling engine coolant. Most of the processes have employed filtration, ion exchange or distillation techniques in various forms. Distillation of used engine coolant alone sometimes produces an acceptable end product; however, it is an expensive, energy consumptive, and relatively slow process which is not suitable for many potential users. Furthermore, distillation equipment is capital intensive and is associated with various workplace hazards. Relatively simple chemical and filtering techniques have been employed apart from and in conjunction with distillation for recovering and recycling used engine coolant. Engine manufacturers have required more thorough purification of the fluid than can be accomplished through simple or chemical filtration methods. This requirement has been underlined in light of advancements in antifreeze chemical inhibitor technologies, and requirements that all pre-existing inhibitor chemistries be removed from the used engine coolant have been imposed.
An early system for recycling engine coolant used xe2x80x9cchemically assisted filtration.xe2x80x9d The concept of this system was that aeration and pH adjustment of coolant would precipitate contaminants, and the addition of chemical additives would restore adequate functionality to permit extended use of the coolant. U.S. Pat. No. 4,946,595 discloses a process for physically and chemically treating used engine coolant of a type which contains one or more glycol and/or alcohol based antifreeze components. The disclosed process includes the steps of oxidation with one or more known oxidizing agents, precipitation with one or more known salt forming agents, and filtration. Chemical additives are added to enhance the oxidation and precipitation. Various corrosion inhibitors and buffering agents are also added to adjust the pH of the recovered solution. However, the appearance of coolant recycled by chemically assisted filtration was commercially unacceptable in many cases. There were also concerns that filtration alone did not provide adequate purification of the recycled coolant.
Another method available for recycling engine coolant is the reverse osmosis (R/O) process, which provides an intermediate fluid that is pure and offers a production rate that is fairly cost-effective compared to distillation (Huff 1992 SAE 921635). The osmosis phenomenon is observed in nature as a distribution or equalization behavior of naturally occurring chemicals. The R/O process for recycling engine coolant has been described in detail in the literature (Eaton etal, 1997 SAE 971773). U.S. Pat. No. 5,167,826 discloses an apparatus and a process for purification of engine coolant by reverse osmosis, and a process for reinhibition with anti-corrosion inhibitors and buffering agents common to antifreeze manufacturing. Reverse osmosis is a faster and more economical method of coolant recycling than distillation, and provides far better purification than filtration.
There are, however, shortcomings to the R/O process for recycling used engine coolant described in U.S. Pat. No. 5,167,826. In particular, when oil or similar petroleum products enter the R/O system, they coat the membranes, xe2x80x9cblindingxe2x80x9d them, and reducing production of recycled coolant to a trickle. In addition, recycling engine coolant by the R/O system alone does not decrease conventional inhibitor anions in the coolant to a level that would permit reinhibition of the intermediate fluid either with traditional, inorganic technologies, or European style carboxylate inhibitors.
Thus, there has been a need for a way to provide a highly purified recycled engine coolant at a cost advantageous compared to virgin coolant.
Briefly stated, the invention in a preferred form is an apparatus and a process which is employed for recycling the glycol and water components of used engine coolant. The used engine coolant is treated through a sequence of purification processes to result in a final recovered, pure fluid that consists of water, ethylene glycol with or without propylene glycol, and less than 0.001 weight percent contaminants.
The used engine coolant is filtered to remove various particulate substances, using one or more filters in series along a flow path. If more than one filter is used, the filters may be of decreasing pore size along the flow path. The filtered coolant is then introduced into a dissolved air floatation separator, a hydrocyclone separator, or a filter press to remove petroleum contaminants (oils and fuels) and particulates from the filtered coolant. The dissolved air floatation separator and hydrocyclone separator may be used together in series. The removal of petroleum contaminants and particulates is extremely important for trouble-free operation for the membrane separation steps (semi-permeable nano filtration and reverse osmosis). The fluid, now purified of oils, grease, fuels, and larger particulates is collected in a holding tank where it is pressurized to a pressure in the range of 50 to 1200 psi, more particularly 100 to 800 psi, or even more particularly 350 to 600 psi and then passed through a semi-permeable nano filtration device whereby glycol and water are separated from the remaining fluid by a semi-permeable nano filtration process. The nano filtered filtrate is collected in a permeate holding tank. The concentrate material separated from the filtrate is returned to previous holding tank for additional passage through the semi-permeable nano filtration device. The filtrate in the permeate holding tank is repressurized to a pressure in the range of 50 to 1200 psi, more particularly 50 to 800 psi, or even more particularly 50 to 300 psi, and passed through a semi-permeable reverse osmosis device, whereby glycols and water are further purified. Concentrate separated from the purified glycols and water is passed back to the permeate holding tank for additional passage through the reverse osmosis process. The permeate is now clear in appearance, but contains anionic contaminants from tap water (for example, chlorides) and from the old inhibitors (for example, nitrite and borate). The recovered glycol and water (permeate) are transported to the continuous electrolysis deionization unit (CDI). The CDI reduces the concentration of undesirable anions in the permeate. Trace contaminants remaining may be removed by distillation, or purification through a dual-bed deionization device, resulting in a solution of 99.999% pure water/glycol coolant base fluid.
The recycled coolant is purified sufficiently to meet ASTM coolant standards when properly reinhibited. Such ASTM standards are found in xe2x80x9cD 3306-98 Standard Specification for Ethylene Glycol Base Engine Coolant for Automobile and Light Duty Service,xe2x80x9d American Society for Testing and Materials, West Conshohocken, Pa. and xe2x80x9cD 6210-98 Standard Specification for Fully-Formulated Ethylene-Glycol Base Engine Coolant for Heavy-Duty Engines,xe2x80x9d American Society for Testing and Materials, West Conshohocken, Pa., both of which are incorporated herein in their entirety by reference.
The D 3306-98 standard specification requires that ethylene glycol base engine coolant concentrate shall consist essentially of ethylene glycol and shall contain suitable corrosion inhibitors, a foam suppressor, and sufficient water to dissolve the additives and to provide a packaged product that can be poured at temperatures as low as xe2x88x9218xc2x0 C. (0xc2x0 F.). The D3306-98 standard specification permits other glycols such as propylene and diethylene to be included up to a maximum of 15% if the chemical and physical properties are met. The physical, chemical and performance requirements of the D 3306-98 standard specification are shown in FIG. 5. Solutions for actual service should be prepared with municipal (treated) water, or a low mineral content well water. If such water is not available, then deionized (demineralized) or distilled water may be used.
The D 6210-98 standard specification covers the requirements for a fully-formulated ethylene-glycol-base coolant for cooling systems of heavy-duty engines, and are intended to cover the requirements for engine coolants prepared from virgin or recycled ethylene glycol. The D 6210-98 standard specification requires that concentrated coolant shall meet all of the requirements of Specification D 3306 (D 3306-98 standard specification) and prediluted coolant shall meet all the requirements of Specification D 4656. The coolant concentrate mixed with water or the prediluted coolant, when maintained with maintenance doses of SCA in accordance with the engine manufacturer""s recommendations, and those on the product label, shall be suitable for use in a properly maintained cooling system in normal service for a minimum of one year. The D 6210-98 standard specification also requires that the coolant shall provide protection in operating engines against cavitation corrosion, also termed liner pitting, and against scaling of internal engine hot surfaces. Hot surfaces typically are within the engine head, head space, or liquid cooled exhaust manifold. Further, both the concentrated and prediluted coolants shall contain less than 50 ppm sulfate ion. Concentrated coolant must contain less than 4% total dissolved solids as measured using Modified Federal Method 2540C, xe2x80x9cTotal Dissolved Solids Dried at 180xc2x0 C.,xe2x80x9d Standard Method for the Examination of Water and Wastewater, American Public Health Association et al., 1015 15th Street, N.W., Washington, D.C. 20005. Prediluted coolant must contain less that 2% total dissolved solids using the same method.
A sufficiently low chloride content is one of the most difficult standards to meet for recycled coolant, and achieving a low chloride content may be difficult and expensive. In the present invention the recycled coolant may comprise chloride in an amount of less than 50 ppm, less than 40 ppm, less than 35 ppm, less than 33 ppm, less than 30 ppm, less than 25 ppm, less than 20 ppm, less than 15 ppm, less than 10 ppm, less than 9 ppm, less than 8 ppm, less than 7 ppm, less than 6 ppm, less than 5 ppm, less than 4 ppm, less than 3 ppm, less than 2 ppm, or less than 1 ppm.
An object of the invention is to provide a new and improved apparatus and process for commercial recycling of used engine coolant.
Another object of the invention is to provide a new and improved apparatus and process wherein used engine coolant may be recycled in a relatively inexpensive and efficient manner.
A further object of the invention is to provide a new and improved apparatus and process for recovering used engine coolant which, upon addition of suitable additives, results in a recycled coolant composition having effective corrosion inhibitor properties, effective freeze and boil protection properties, a pH between approximately 8.0 and 10.5, and additional properties which satisfy standard specifications for new and recycled engine coolant.
A further object of the invention is to advance the purification technology of the apparatus and process to permit the transformation of coolant inhibited with xe2x80x9cconventionalxe2x80x9d (inorganic) inhibitor technologies to coolant that may be inhibited either conventionally or with carboxylate technologies often referred to as xe2x80x9cextended servicexe2x80x9d or xe2x80x9clong lifexe2x80x9d inhibitor systems.
A yet further object of the invention is to provide a new and improved apparatus and process for recycling engine coolant which apparatus and process are capable of separating a much higher volume of pure glycol and water from the used engine coolant and does not require distillation or other energy consumptive processes.
Other objects and advantages of the invention will be apparent from the drawings and the specification.